Ten gigabit Ethernet (“10 GbE”) is a version of Ethernet with a nominal data rate of 10 Gbit/s (billion bits per second). This standard defines full duplex point-to-point links, which are generally connected by network switches.
There are different transmission mediums that may carry a 10 GbE signal. One transmission medium is optical fiber. Various protocols define how a 10 GbE signal is to be carried over optical fiber, including 10GBASE-SR, 10GBASE-LR, and other such standards.
Another transmission medium is copper wiring. With copper wiring, a 10 GbE signal may be carried over twinaxial cabling, twisted pair cabling, and backplanes. A backplane (or “backplane system”) is generally considered a group of connectors connected in parallel with each other, so that each pin of each connector is linked to the same relative pin of all the other connectors forming a computer bus. Standards that define 10 GbE transmission over a backplane include 10GBASE-KX4, 10GBASE-KR, and 40GBASE-KR4. These standards are defined by the Electrical and Electronics Engineers (“IEEE”) 802.3 working group. In particular, these standards are defined by IEEE 802.3 clause 74.
One of the difficulties in communicating over copper wiring, and over a backplane system in particular, is that the transmitted bitstream may be corrupted when it reaches its destination. To compensate for errors in the transmitted bitstream, IEEE 802.3 clause 74 proposes a forward error correction (“FEC”) coding technique.
In communication, forward error correction (FEC) is a coding technique used for controlling errors in data transmission over unreliable or noisy communication channels. The principle behind FEC is that a transmitter encodes its message in a redundant way by using an error-correcting code (ECC). The redundancy in the FEC encoded bitstream allows a receiver to detect an error that may occur in the bitstream, and then correct this error without retransmission. Under IEEE 802.3 clause 74, an FEC encoded bitstream typically contains datablocks of 2112 bits (32 datawords of 64 bits each plus 32 parity bits).
However, while an FEC encoded bitstream allows a receiver to recover erroneous blocks, there may be problems in the communication link that generated those errors. So long as the errors exist in the communication link, transmitted bitstreams may continuously include erroneous bits. By allowing the cause of the erroneous bits to persist, the likelihood increases that the receiver receives an unrecoverable bitstream and that vital communications may be delayed as a result.